Trunking with leaky feed system

Post by **wavetar** » Tue Dec 11, 2001 4:46 pm

OK, here's my scenario. We are looking at upgrading a system on an oil drilling platform. They currently have 2 UHF MTR2000 conventional repeaters, and are using a multiple-run leaky feed antenna system which apparently works quite well (after much time spent optimizing, so we're told). What they want is to have at least 7 separate channels for their radios to operate on, multiple PL or DPL is not an option they desire. So, the easiest but most expensive option is to add another 5 repeaters, nice sale. The other option being discussed is to convert the 2 existing MTRs and make them part of a 3 channel Startsite trunking system. Less cost & equipment, and it'll give them what they want plus the many added trunking features.
My immediate thought on that is we may run into many strange problems (timing issues, data collision, etc) due to using the multiple-run leaky feed system. I've never seen nor heard of anyone using trunking with this set-up. I think we may be better off with the simpler, 5 extra conventional repeaters option. Has anyone here had any experience with this? I'd welcome any comments, experiences, or theories on the matter. Also, any known sites containing decent information regarding leaky feed theory would be appreciated as well. Thanks,

Todd

RFdude · Post by **RFdude** » Tue Dec 11, 2001 7:08 pm

I don't think you will have any problems at all especially if your "distributed antenna" system is passive (only has splitters). The distances around an oil rig won't pose any concerns from an RF propagation delay perspective.

What can cause bit bashing in a "simulcast" scenario is two fold: 1) transmitters that are not on exact frequencies/offsets... in your case you only have one transmitter per channel so you are OK, and 2) audio/data delays over your transport media... we are talking many microseconds to start destructive interference depending on your data rate or supervisory tone frequencies. For a passive system your only delays are propagation through the cable and over the air... no problem.

Things like On-Frequency-Repeaters or enhancers that have single channel CRYSTAL filters can introduce enough propagation delay to start degrading your service. But enhancers with SAW band pass filters or simple amplifiers with conventional duplexing or filtering are OK for your application as they introduce negligable delay (nanoseconds).

Does this sound like the info you are looking for? If you have any specifics in mind, throw it into the forum and the BORG wisdom will help you.

RFDude.

raymond345 · Post by **raymond345** » Tue Dec 11, 2001 8:03 pm

Leaky feeder systems have been here for 15 years.EL-Equip in Sudbury ontario canada
is one of the dealers for this system.
It works very well.
Raymond eMail [email protected]

Post by **wavetar** » Wed Dec 12, 2001 5:04 am

Thanks for the replies so far guys, especially RF Dude. I'm still hoping someone out there has seen trunking done in a similar set-up, I'd hate to have to work on a "Guinea Pig" system, although sometimes it's what you end up doing in this line of work! Thanks again.

Todd

---edit---
Thanks to Raymond as well, I found El-Equip's website & find it to be very informative.

<font size=-1>[ This Message was edited by: wavetar on 2001-12-12 08:28 ]</font>

bemus · Post by **bemus** » Fri Dec 14, 2001 12:33 pm

we have a 4 chan trunked site on leaky coax in a power plant. works fine

Post by **wavetar** » Fri Dec 14, 2001 6:49 pm

Guys, thank you very much. You have set my mind at ease in this regard. We have now also taken a closer look at this system as it exists & see several ways to improve it, which will also minimize any troubles I was anticipating. This board is great.

Todd

Post by **/\/\y 2 cents** » Mon Dec 17, 2001 12:49 am

Put a leaky feed system on a cruise ship..worked fine...just distribute the cableing as needed....for in-house comms where there are thick walls sometimes its the best alternative....Also check out NY Subway police....or transit or something....this is what they have had for 20 years underground and apparently it works great.